Empty container detection using container side pressure sensing

ABSTRACT

A system and method for monitoring changes in the pressure of a fluid line upstream of an infusion pump to determine when a fluid container has emptied, and to provide a signal indicating that the container needs replacement or replenishment. The difference between averaged pressures over separate time periods is monitored to determine when the fluid container is empty. The system and method are applicable to primary and secondary fluid container setups and can detect the point where the secondary has been emptied and the primary flow has resumed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a system and method fordetermining when an infusion fluid container has emptied, or is about toempty, as a result of fluid being withdrawn from the container. Morespecifically, the present invention relates to a system including aninfusion pump having a sensor that is capable of monitoring anddetecting pressure within the container-side of a fluid “infusion set”so as to determine when the associated fluid container is empty, orabout to become empty. Upon such detection, the system may provide alocal or remote audible and/or visual alert to a caregiver administeringor monitoring the infusion and may initiate pre-programmed changes tothe flow of fluid including changing to an alternate flow rate orstopping infusion.

2. General Background and State of the Art

Infusion of therapeutic fluids to treat or nourish patients is commonlyused in hospitals and other medical care institutions. Originally suchinfusions were carried out by hanging a bag or container of therapeuticfluid from a pole so that fluid flows under the force of gravityregulated by a user-controllable restrictor through a length of tubingand into the lumen of a vessel of a patient. More recently, the flow offluid into the patient is under the control of a programmed infusionpump located in the fluid pathway. Infusion pumps are useful in thatthey allow for more precise control of the flow of therapeutic fluidinto the patient. For example, using an infusion pump, relativelyprecise amounts of fluid may be infused at controlled rates. Moreover,the rate of infusion may be altered during the infusion by programmingthe pump to pump the fluid at a different rate. This capability isuseful where a bolus of therapeutic fluid is desired to initiate aninfusion regimen, with the rate then being decreased to a reduced flowrate for the remainder of the infusion. When a pump is located in thefluid pathway, the portion of the tubing between the container ofmedical fluid and the pump is referred to as the “container-side” fluidline.

One problem that exists with all infusions is that it is difficult tomonitor and determine when the fluid container becomes empty,necessitating a change of container or other attention from acare-giver. In the case of a simple primary infusion, when the fluidcontainer is emptied, the flow rate is typically reduced from the flowrate prescribed by a physician to a “keep vein open” or KVO rate. If theempty or nearly empty container is not replaced or replenished, air mayenter the infusion line, which is generally considered to be anundesirable condition. In the case of “secondary” infusion, a fluidcontainer containing a different IV solution is attached to thecontainer-side primary fluid line and its fluid is infused temporarilyin lieu of the primary fluid until the secondary container is empty. Inthese infusions attention must be given to the secondary fluid containerso that air does not enter into the infusion line.

One method used to monitor the state of the fluid container has been toestimate the volume of fluid in the secondary container and program thesecondary mode of the pump to deliver this volume. This method is proneto errors due to mistakes or inaccurate estimations of the fluidinfusion rate or the amount of fluid remaining in the container.

In many secondary infusion systems, a one-way check valve is inserted inthe primary fluid path and the primary container is lowered below thesecondary container, typically, for example, about eight inches. Thesecondary fluid enters the main intake fluid pathway through a port inthe main fluid line. When the secondary container is filled, thepressure exerted against the check valve prevents flow of the primaryfluid into the fluid line. When the secondary fluid container is emptiedto a level slightly below that of the top of the fluid in the primarycontainer, the pressure against the check valve reduces to the pointthat it opens, permitting the primary fluid to once again flow into theinfusion line.

In many cases where secondary infusion of a fluid is performed, thedesired rate of secondary fluid flow is different from the desired rateof primary fluid flow. Accordingly, an operator must preset the infusionpump with the estimated volume in the secondary container, so that whenthe pump has infused that amount at the prescribed secondary rate, thepump will automatically transition to the primary flow rate. However,frequent errors due to incorrect estimation of container volume orinaccurate setting of the secondary volume-to-be-infused renders thismethod unreliable, requiring frequent monitoring by care-givers toensure that the proper fluid is being infused at the proper rate, and toprevent air from entering into the infusion line in the instance of afault such as a non-flowing checkvalve.

In some infusion tubing setups, there may be multiple infusion linesconnected together via a manifold or similar device providing fluid to acommon vascular access device. Such a system allows two or moretherapeutic fluids to be infused into the patient in a programmedsequence. For example, the care-giver may prescribe a therapeuticregimen requiring the infusion of a primary fluid for a first set lengthof time, a secondary fluid for a second set length of time, and then athird fluid for a third set length of time, followed by infusion of thesecondary fluid. In many cases, the various therapeutic fluids are notcompatible with each other, and so care must be taken to avoid mixingthe fluids in the manifold. While current pumps can be programmed todeliver the exemplary therapeutic regimen described above, as with theother examples, errors in setting the pumps for the volumes to beinfused, or the occurrence of an empty container, can complicate thedelivery of the infusion fluids and require frequent monitoring duringthe infusion.

Another attempt to determine when a container is empty involved tryingto sense the vibration produced by drops falling into a drip chamber.Cessation of these vibrations meant that drops were no longer falling,indicating that the container was empty. However, noise sources such aspatient or equipment movement, cross coupling between fluid lines orpumping channels made this approach difficult to carry out in practice.

What has been needed, and heretofore unavailable, is an inexpensive yetreliable system and method for detecting when an infusion container isempty, or nearly empty, and for providing a signal to an infusion pumpto either alter the infusion rate, provide an alert signal to acare-giver that the container needs replenishment or replacement, orswitch to a different infusion source. What is further needed is areliable system and method for use with automatic secondary infusionsetups that provide detection of the occurrence of transition from flowof the secondary fluid to flow of the primary fluid. The presentinvention satisfies these and other needs.

INVENTION SUMMARY

Briefly and in general terms, the system and method in accordance withthe invention are directed to monitoring the pressure of a fluid lineconnecting a fluid container with an infusion pump. A pressure sensormonitors the pressure within the fluid line as fluid is drawn from thefluid container by the infusion pump. A processor in communication withthe pressure sensor samples at a selected frequency pressure signalsgenerated by the pressure sensor representative of the pressure withinthe fluid line. At the conclusion of a selected period of time, theprocessor averages the values of the sampled pressure signals receivedduring the period of time, and stores the averaged value in a memorythat is accessible by the processor. After a second period of time haselapsed, a second averaged value is calculated using the sampled signalsreceived during the second period of time. The processor then comparesthe averaged value from the second period of time to the averaged valuefrom the first period of time to determine if there is a difference thatreaches a predetermined threshold. If the predetermined threshold isexceeded, the processor provides a signal indicating that thepredetermined threshold has been exceeded.

In another aspect, the present invention is embodied in a system fordetermining when a fluid container connected to an infusion pump by aninfusion line has been emptied of fluid and comprises: a pressure sensorin operable communication with the fluid line, the pressure sensorcapable of monitoring a pressure within the fluid line and providing asignal representative of the monitored pressure; a memory for storingpressure-related values; and a processor in operable communication withthe pressure sensor and the memory, the processor programmed to receivesignals from the pressure sensor and sample the received signals atselected intervals, the processor also programmed to calculate a firstaveraged sampled pressure value from the signals received during a firstselected interval and store the first averaged sampled pressure value inthe memory, the processor also programmed to compare the stored averagedsampled pressure value with a second averaged sampled pressure valuecalculated during a second selected interval and provide a signal if thecomparison results in a difference between the first and secondcalculated averaged sampled pressure values reaches a predeterminedthreshold. In a more detailed aspect, the pressure sensor is locatedwithin a housing of the infusion pump. In further detail, the processoris also located within the housing of the infusion pump and in yet evenfurther detail, the processor is located at a position remote from theinfusion pump.

In still another aspect in accordance with the invention, a system isprovided wherein the processor is in communication with an informationsystem of an institution, and wherein the signal is communicated to theinformation system for dissemination to at least one care giver withinthe institution. In another embodiment, the processor is part of a localnetwork.

In a further more detailed aspect, the sampling period is determined bycounting the number of pump mechanism cycles that have occurred, andthen calculating the averaged value when a selected number of cycleshave been completed.

In yet another aspect in accordance with the invention, a method isprovided for detecting when a fluid container has emptied during thecourse of an infusion. The method comprises the steps of sampling thepressure within an infusion line connecting a fluid container with aninfusion pump at a selected frequency, calculating a first averagedsampled pressure value by averaging the sampled pressure over a selectedperiod of time, storing the averaged sampled pressure value in a memory,calculating a second averaged sampled pressure value by averaging thesampled pressure over a second selected period of time, calculating adifference between the first averaged sampled pressure value and thesecond averaged sampled pressure value, and providing a signal if thedifference reaches a pre-determined threshold value. In another aspect,the method further comprises the steps of continuously sampling thepressure within the infusion line and calculating averaged sampledpressure values, incrementing the selected period of time for eachcalculation, comparing the latest averaged sample pressure value to aselected previous averaged sampled pressure value and calculating adifference between the latest averaged sample pressure value and theselected previous averaged sampled pressure value, and providing asignal if the difference reaches a pre-determined threshold value.

In a further aspect, the step of providing a first signal comprisesproviding an indication that the container is empty. In another aspect,the step of providing the second signal comprises providing anindication that a drip chamber associated with the container is empty.

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, which illustrate, by way of example, the featuresof the invention

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an infusion set-up including a fluid source and aninfusion pump for infusing fluid from the fluid source into a patient.

FIG. 2 is a schematic side view of an exemplary peristaltic infusionpump including an upstream pressure sensor.

FIG. 3 is a schematic block diagram of one embodiment of an infusionpump controller capable of being programmed to carry out the presentinvention.

FIG. 4 depicts an infusion set up showing a container, drip chamber,infusion line and infusion pump with a container side (upstream)pressure sensor, and a graph of sampled pressure measurements over timeas fluid is withdrawn from the chamber, the graph illustrating thedetection of an empty container in accordance with one embodiment of thepresent invention.

FIG. 5 shows an infusion set up with primary and secondary fluidcontainers both connected to the same fluid line to infuse fluid to thepatient, showing that the secondary container is higher than the primarycontainer.

FIG. 6 presents a graph of the pressure waveform of the system of FIG.5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1. there is shown an infusion pump set-up,generally designated 10, shown in use in its intended environment. Inparticular, the infusion pump set-up 10 is shown mounted to anintravenous (I.V.) pole 12 on which a fluid source 14 containing an I.V.fluid is held. The fluid source 14 is connected in fluid communicationwith an upstream fluid line 16. The upstream fluid line 16 is aconventional I.V. infusion-type tube typically used in a hospital ormedical environment, and is made of any type of flexible tubingappropriate for use to infuse therapeutic fluids into a patient, such aspolyvinylchloride (PVC). The upstream fluid line 16 is connected withanother tube portion 18 that is flexible and is mounted in operativeengagement with a peristaltic pumping apparatus 19, for propelling fluidthrough a downstream fluid line 20, for example, to a patient's arm 22.It will be understood by those skilled in the art that the upstreamfluid line 16, the flexible portion fluid line 18, and the downstreamfluid line 20 may be portions of a continuous length of flexible tubing,with the portions defined by the location of the peristaltic pump 19.For convenience in reference, the overall length of tube has been giventhe reference numeral of 21 in FIGS. 1 and 2. In this context, the term“upstream” refers to that portion of the flexible tubing that extendsbetween the fluid source and peristaltic pump, and the term “downstream”refers to that portion of the flexible tubing that extends from theperistaltic pump to the patient. For convenience, the overall tubeextending between the

FIG. 2 depicts an enlarged schematic view of the pumping mechanism ofthe infusion pump 10 showing the interaction of the infusion tube withthe elements of the peristaltic infusion pump. The fluid line 16 isdisposed in the housing 30 of the pump 10 in such a manner that theflexible portion 18 of the infusion line is in releasable contact withone or more fingers 40 of the peristaltic infusion pump. Typically, sucha peristaltic infusion pump utilizes a camshaft 35, or other mechanism,to actuate one or more fingers 40 so that one or more fingers 40sequentially press upon and squeeze the flexible portion 18 of the tubeto displace fluid within the tube in a downstream direction. Thedownstream segment 20 of the tube of the fluid administration set 21 isalso partially shown. Various details of a complete peristalticmechanism have been left out of FIG. 2 so that clarity of illustrationof the above-discussed features is retained. However, one skilled in theart will understand that many other mechanical components can exist withsuch a mechanism.

An upstream pressure sensor or detector 50 is mounted in the housing ofthe pump 10 to monitor the fluid pressure within the upstream tube 16.The upstream pressure sensor 50 may be any kind of detector known in theart that is capable of monitoring the fluid pressure within the tube 16and providing signals that may be received by suitable electronics, suchas, for example an A/D converter and a storage medium, such as a flashmemory, or other type of suitable storage medium for storing digitalvalues representative of the signals provided by the sensor. The signalsmay also be provided to a computer or microprocessor for analysis,display or reporting. Examples of pressure sensors or detectors suitablefor monitoring the pressure within an upstream infusion line are siliconstrain gauges, resistive strain beams or other sensors or detectorsknown to those skilled in the art.

Those skilled in the art will also understand that the upstream pressuresensor 50 and methods described herein are equally applicable to anydisplacement type infusion pump, and such is intended to be within thescope of the present invention. Even further, the principles may beemployed even in pumps or servo-controlled gravity flow regulators.Moreover, while the present invention is described in relation to aninfusion pump having a processor or computer associated with the pump,it is intended that the invention also include systems wherein themicroprocessor or computer is remote from, but in communication with thepump.

Generally, as shown in FIG. 3, the infusion pump 10 will include acontroller 70 configured or programmed to control the operation of theperistaltic infusion pump so that a prescribed amount of medication orother therapeutic fluid is infused into the patient over a desiredperiod of time. Such controllers typically include a microprocessor 75,a memory 80 associated with the microprocessor 75, one or more inputs 85for inputting signals to the microprocessor, and one or more outputs 90for outputting signals from the microprocessor.

The controller 70 may also be in communication with other systems, suchas a pharmacy information system, hospital administration system, orother such systems in the institution using an input/outputcommunications port 92 and a communication means 95. The input/outputcommunications port 92 may be any port configured to send and receivedata using appropriate communication protocols, such as RS232 and thelike. For example, the input/output communications port 92 may be aserial port, a parallel port, a USB, or other suitable port. It willalso be understood that the input 85 and the output 90 may be combinedin such a manner that all signals to and/or from the processor arecommunicated through one or more input/output ports 92, rather thanthrough separate inputs and outputs.

The communication means 95 may be a hard wired or wireless connection toanother computer, a local area network, a wide area network, a telephoneline to a remote server or client system, or the Internet. Thecommunication means may include specialized connection devices forconnecting to optical fiber, coaxial cable, Ethernet cabling, or othercommunication lines. Alternatively, wireless connections may be used,which may also include the use of suitable transmitters and receivers asis known in the art. Such wireless connectivity may include use of infrared, RF, Bluetooth or WiFi (IEEE 802.11b) communication means and thelike. Additionally, the microprocessor 75 is commonly programmed usingeither embedded programming instructions or suitable software so thatthe microprocessor can carry out the tasks desired of it.

In one embodiment of the system and method of the present invention, themicroprocessor 75 is capable of receiving signals from an upstreampressure sensor 105 through the input 85 (typically an amplifier and A/Dconverter). The upstream pressure sensor 105 is disposed adjacent anupstream infusion line so as to monitor the pressure within the upstreaminfusion line, and provide signals representative of the sensed pressurewithin the infusion line to the microprocessor 75. The microprocessor75, as described above, is programmed using appropriate software orembedded commands to analyze the signals received from the upstreampressure sensor 75. After analysis of the received upstream pressuresignals is completed, the processor may output a signal through theoutput 90. This signal output may be directed to the pump motor 115 tocontrol the infusion of fluid to the patient.

The output signal may also be directed to a display 120 to inform anoperator of the status of the pump and/or the pressure within theupstream infusion line. This display may also include a means ofproviding a visual alert, such as a flashing display, blinking light, ora change in text color on the display to alert an operator that theinfusion set-up requires attention.

The output signal may also be directed to an alert module 125. Thisalert module may be a separate module of the processor 75 that iscontrolling the pump 10, or it may be located at a location remote fromthe pump, and/or associated and in communication with a separateprocessor remote from the pump. The alert module 125 may be configuredto provide visual, auditory, or a combination of visual and auditorynotifications to care givers to alert the care giver that attention mustbe given to the infusion system. The alert module may produce signalsthat are communicated to consoles at the bed side, the nurse station, ora centrally located monitoring system. Additionally, variouscombinations of display changes and auditory alerts may be used tosignify a priority of an alert, so that alerts which do not requireimmediate attention are less noticeable than alerts that requireimmediate attention to correct a problem before harm to the patientbeing infused can occur.

The alert module 125 may also provide signals representing the progressof the infusion, including any alerts generated due to a sensed reducedor negative pressure in the upstream infusion line 16 (FIG. 1), to adatabase where the information is stored for later inspection andanalysis. The database may be associated with the pump 10, or thedatabase may be remote from the pump. For example, where the pump iscontrolled by a remote controller, the database may be located andassociated with the remote controller. In another embodiment, thedatabase may be part of an institutional information system which may bepart of an enterprise wide network.

In another embodiment, the microprocessor 75 may also be configured toreceive signals from a pump motor sensor 110 through the input 85. Inthis embodiment, the processor 75 may monitor the function of the pump,collecting, analyzing, and storing information related to the infusion,such as, for example, the start time and completion time of theinfusion, the amount of fluid infused, and the number of pump cyclesthat have been completed since the start of the infusion or since aselected time in the past. This information may be stored in the memory80 for later retrieval and analysis, or the information may becommunicated to another, remote, system using the communication means95.

FIG. 4 illustrates the design and software analysis of an embodiment ofthe present invention. In this embodiment, the upstream portion 200 ofan infusion setup is shown. Such an infusion set up typically comprisesa fluid container 205 that is filled with an I.V. fluid. To facilitatepriming of the infusion set, avoid entrainment of air bubbles andprovide visualization of the infusion, a drip chamber 210 is generallylocated adjacent the bottom of the container 205. A length of flexibleinfusion line extends from the bottom of the drip chamber and into theinfusion pump 220. The infusion pump 220 includes an upstream, orcontainer side pressure sensor 225, and typically also includes apatient side pressure sensor 230 as well as a pumping mechanism 222,such as a peristaltic mechanism.

As fluid is withdrawn from the container 205, the level of fluid falls.The upstream pressure sensor 225 in one embodiment senses the resultingdecrease in pressure within the infusion line 215. The pressure withinthe infusion line 215 is dependent on the amount of fluid in thecontainer 205 and the rate of flow of fluid through the fluid line.

The change in pressure within the infusion line 215 as an infusionprogresses is illustrated by the graph in FIG. 4. During an infusion,the processor controlling the infusion pump motor also samples theoutput of the upstream pressure sensor 225. Typically, the upstreampressure sensor is sampled about once every 100 milliseconds, althoughother sampling rates may be used. Because the mechanism 222 does notdraw fluid absolutely smoothly, small variations of intake flow ratethroughout a mechanical cycle through the fluidic impedance to flow ofthe upstream tubing 215 produce small pressure changes in the upstreaminfusion line 215. The amount of fluid pumped during a cycle isdependent on the particular pump being used. For example, the MEDLEY®Large Volume Pump Module (LVP) manufactured and sold by ALARIS MedicalSystems, Inc., San Diego, Calif., typically draws and expels 165microliters of fluid volume during each cycle.

In one embodiment of the present invention, the upstream sensor 225 issampled synchronously with the movement of the pump mechanism 222 toaccount for artifacts in the pressure signal caused by the variation inflow during a cycle. Since the fluctuations are cyclic with eachrevolution of the mechanism of the infusion pump 220, the cycle averagedpressure (“Pca”), which is an average of the sampled pressures detectedby the pressure sensor during a single cycle. Pca is highly stable fromcycle to cycle owing to the large number of samples typically measured.One added advantage of averaging the signal is that the averaging maystart and stop at any point within the cycle and the averaged signalwill produce equivalent results to calculations begun and ended at adifferent point. Further, pausing the pump, or changing the pumping ratewill not affect the resultant Pca value. In a typical embodiment, thepressure sensed by the upstream pressure sensor 225 is sampledapproximately 100 times per cycle. Thus, in the MEDLEY® LVP pumpidentified above, a pressure sample is obtained for about each 1.5-2.0microliters of fluid drawn from the container.

The pressure sampling and analysis process is controlled by theprocessor associated with the infusion pump. As each sampled pressure isreceived by the processor, the processor may store the sampled pressurevalues in a buffer, cache, working memory, or other storage medium forlater analysis. Periodically, typically at least once a cycle, thesampled pressure values are averaged to calculate the Pca. The valuesfor the Pca signal may also be stored by the processor for furtheranalysis, as will be disclosed in more detail below. Each stored Pcasignal may also be associated with a value representing the number ofcycles that had elapsed since the start of the infusion, or since thelast Pca was determined. For example, the first Pca calculated could beassociated with the number 1, the second Pca with the number 2, and soon, so that the series of Pca may be sequentially arranged in accordancewith the number of cycles that are completed, providing a time frame forfurther analysis to determine the occurrence of sequential events.

As an infusion fluid container empties, the “head” pressure due to depthof the fluid within the upstream infusion line falls slowly, as can beseen from the line indicated by numeral 250 of the graph of FIG. 4,which is a line connecting pressure measurements indicated by volts ateach sample. The sampled signal from the pressure sensor 225 may befurther processed by calculating the difference between two Pca signalsseparated by one cycle. The “delta” value thus calculated is the slopeof the Pca filtered pressure signal of line 250, and is illustrated bythe line indicated by numeral 255 of the graph of FIG. 4, which showsthe slope or rate of change or differential in units of volts persecond. Differentiating the Pca signals in this manner is advantageousin that it enhances the sensitivity of the analysis, since for smallcontainers, the pressure changes much more rapidly than the pressurewhere large fluid containers are used, and such large changes inpressure may result in false identification of an empty container, aswill be discussed in more detail below.

Referring again to the graph of FIG. 4, the function of one embodimentof the present invention will be described. As fluid is removed from thecontainer 205, the pressure within the fluid line 215 falls slowly andrelatively constantly, as indicated by the line 250 of the graph. It isalso apparent that the slope of the pressure drop is relativelyconstant, although magnification of the slope value by the choice ofunits on the axis of the graph causes the graph of the slope to appearsomewhat jagged. The processor associated with the pump monitors thevalue of the slope, or delta signal, of line 250 that have beencalculated as described above, and is typically programmed to ignore allchanges in the slope of the signal that fall below a pre-determinedthreshold.

Because the amount of fluid being withdrawn from the container 205 bythe pump 220 is relatively small compared to the volume of fluid withinthe container 205, the level within the container 205 falls relativelyslowly. However, when the fluid surface level reaches the orifice of thedrip chamber 210, which typically has less volume than the container205, the amount of fluid removed during each sensor sampling results ina relatively large change in fluid level with each sample. This rapidreduction in the level of the fluid appears as a large negative deltasignal at point b′ of line 255. Similarly, once the drip chamber 210empties, the fluid surface level enters the relatively small bore of theinfusion line 215, resulting in a further pressure decrease and largenegative delta, depicted at point c′ on line 255.

As stated above, the processor 75 monitoring the pressure signal may beprogrammed to respond when a negative delta signal reaches apre-determined threshold value, as illustrated by the line 260 of thegraph of FIG. 4. When the delta signal reaches the threshold valuerepresented by line 260, the logic of the processor is programmed todetermine that the container has emptied. The processor may respond tosuch a threshold-exceeding event in a number of ways known to thoseskilled in the art, such as providing a visual or audible signal to acare-giver indicating that the infusion system needs attention.Alternatively, the processor may log the event in a memory that may beeither associated with the processor, or located at location remote fromthe pump or processor, if the processor is in communication with anappropriate storage media by way of a network connection or some othermeans.

In another embodiment, the processor 75 may respond to a sufficientlylarge delta signal indicating an empty container 205 by operating one ormore suitable valves to change containers, or to change between infusionlines or infusion sources or take another suitable action depending onthe type of infusion regimen that has been programmed into the processorassociated with the pump 220. This is particularly useful where morethan one infusion line or source is connected to the pump by way of amanifold or other similar arrangement. For example, where the systemdetects that a secondary infusion container has been emptied, theprocessor may provide a command to the pump to change the rate ofinfusion to a keep-vein-open mode, or it may control the pump to beginpumping at a different rate suitable for infusion of fluid from theprimary container.

In another embodiment, the processor 75 may store the occurrence ofthreshold exceeding delta signals so as to discriminate between theemptying of the container 205 and the emptying of the drip chamber 210.In this embodiment, a memory 80 associated with the processor may beindexed with a value indicating the start of the infusion. When thefirst delta signal that reaches a pre-determined threshold is detected,that value, or some representation of that value, or a flag indicatingthat a pre-determined threshold exceeding event has occurred. may bestored in the memory. When a second threshold-exceeding delta signal isdetected, the logic of the processor, by comparing the sequencing of thethreshold exceeding events, can determine which event occurred first intime, indicating that the container 205 is empty, and which eventoccurred later in time, indicating that the drip chamber 210 is empty.Such a determination is useful in ensuring that all, or nearly all ofthe fluid contained in the container 205 is infused into the patient,leaving only the relatively small volume remaining in the upstreaminfusion line 215, before sending an alert to a care-giver or monitorsystem that the container is empty and needs replenishment orreplacement. Further, such determinations may be made by the processordepending on the infusion regimen prescribed. For example, in the caseof a secondary infusion, the processor is able to determine when thesecondary container is empty, and infusion switches to a primarycontainer, and when the primary container is empty, so that it mayprovide an alert to the care giver or institution that replenishment orreplacement of the fluid containers is required.

Turning now to FIG. 5, there is shown an infusion set up 270 withprimary 272 and secondary 274 fluid containers both connected to thesame container-side fluid line 276 to infuse fluid to the patient. Boththe primary and the secondary fluid containers include a drip chamber278 and 280 respectively. The primary line 282 includes a check valve284 so that the secondary fluid will flow to the infusion pump 286. Afitting 288 connects the line 290 from the secondary to thecontainer-side fluid line 276. FIG. 5 shows that the secondary container274 is higher than the primary container 272 so that the fluid from thesecondary will activate the check valve 284 to prevent fluid from theprimary from flowing into the container-side fluid line 276. Althoughnot shown, the infusion device 286 includes an upstream pressure sensoras is shown in FIG. 4.

Referring now to both FIGS. 5 and 6, the flow of fluid through theinfusion set up will be shown and the pressure waveform of thecontainer-side fluid line is shown. The line segment 300 represents thepressure of the secondary container 274 which is falling slowly whilethere is fluid surface in the secondary container. When the fluidsurface reaches the drip chamber cannula, as shown at point 310, thepressure will fall more rapidly, as indicated by the line 320. Once thefluid surface is in the drip chamber 280, the fluid pressure falls moreslowly again 330. But when the fluid surface reaches the secondary line290 as shown at point 340, the pressure falls rapidly, as indicated bythe line 350. Once the fluid surface of the secondary line becomes levelwith the fluid surface in the primary container 272, the pressure changebecomes small again as shown by line 360 because now the primarycontainer is emptying. Finally when the primary container is emptied andthe primary fluid enters its drip chamber 278 cannula, a rapid negativepressure drop occurs as shown by line 380.

The waveform of FIG. 6 can be considered to be a sort of “signature” ofwhat is to be expected in a primary/secondary system such as that shownin FIG. 5. If the operator sets a secondary volume to be infused(“VTBI”), then by detecting the failure of this pattern or signature tooccur within a pre-determined volume relative to the programmedsecondary VTBI, a fault of the setup (such as a failure to open a clampon the secondary line 290) could be determined and the operator alerted.Also, if the infusion continues for some selected time period beyond theprogrammed secondary VTBI without the appearance of the “return toprimary” signature shown in FIG. 6, then a fault is determined.

Another use of the waveform, pattern, or signature shown in FIG. 6 is toautomatically switch infusion rates. If the operator does not set asecondary VTBI, then by detecting the occurrence of the pattern of FIG.6, the system will automatically determine that flow from the primarycontainer has resumed. The pump could be automatically programmed tochange its flow rate to the primary flow rate at that time.

While several particular embodiments of the invention have beenillustrated and described, it will be apparent that variousmodifications can be made without departing from the spirit and scope ofthe invention.

1. A method for detecting when a fluid container has emptied during thecourse of an infusion, comprising: sampling the pressure within aninfusion line connecting a fluid container with an infusion flow controldevice at a selected frequency; calculating a first averaged sampledpressure value by averaging the sampled pressure over a selected periodof time; storing the averaged sampled pressure value in a memory;calculating a second averaged sampled pressure value by averaging thesampled pressure over a second selected period of time; calculating adifference between the first averaged sampled pressure value and thesecond averaged sampled pressure value; and providing a signal if thedifference reaches a pre-determined threshold value.
 2. The method ofclaim 1 further comprising: continuing to sample the pressure within theinfusion line and calculating averaged sampled pressure values,incrementing the selected period of time for each calculation; comparingthe latest averaged sample pressure value to a next previous averagedsampled pressure value and calculating a difference between the latestaveraged sample pressure value and the next previous averaged sampledpressure value; and providing a signal if the difference reaches apre-determined threshold value.
 3. The method of claim 2 furthercomprising: processing multiple averaged sample pressure values toprovide an optimized measure of a rate of change of a slope of themultiple averaged sample pressure values, and determining when theoptimized measure of the rate of change indicates the existence of apre-defined condition within the infusion line.
 4. The method of claim 1wherein providing the signal provides an indication that the containeris empty.
 5. The method of claim 2 wherein providing the signal providesan indication that a drip chamber associated with the container isempty.
 6. The method of claim 1 further comprising the step ofsynchronizing the sampling with movement of a pump mechanism that causesthe fluid to flow from the fluid container.
 7. The method of claim 1wherein the step of sampling the fluid pressure comprises the step ofsampling the pressure within an infusion line through direct contactwith the infusion line at a location lying between a fluid movementmechanism in the fluid flow control device and the container.
 8. Themethod of claim 1 further comprising the steps of sampling the pressurewithin an infusion line connecting a primary and a secondary fluidcontainer with a fluid flow control device.
 9. A system for determiningwhen a fluid container connected to an infusion flow control device byan infusion line has been emptied of fluid, comprising: a pressuresensor in operable communication with the fluid line, the pressuresensor capable of monitoring a pressure within the fluid line andproviding a signal representative of the monitored pressure; and amemory for storing pressure related values; a processor in operablecommunication with the pressure sensor and the memory, the processorprogrammed to receive signals from the pressure sensor and sample thereceived signals at selected intervals, the processor also programmed tocalculate a first averaged sampled pressure value from the signalsreceived during a first selected interval and store the first averagedsampled pressure value in the memory, the processor also programmed tocompare the stored averaged sampled pressure value with a secondaveraged sampled pressure value calculated during a second selectedinterval and provide a signal if the comparison results in a differencebetween the first and second calculated averaged sampled pressure valuesreaches a predetermined threshold.
 10. The system of claim 9 wherein thepressure sensor is located within a housing of the infusion flow controldevice.
 11. The system of claim 9 wherein the processor is remote fromthe infusion flow control device.
 12. The system of claim 9 wherein theprocessor is in communication with an information system of aninstitution, and wherein the signal is communicated to the informationsystem for dissemination to at least one care giver within theinstitution.
 13. The system of claim 9 wherein the processor isprogrammed to count the number of revolutions of a fluid movementmechanism of the infusion flow control device, and calculates theaveraged pressure value when a predetermined number of revolutions havebeen completed.
 14. The system of claim 9 wherein the pressure sensor isdisposed in direct contact with the fluid line at a location between afluid movement mechanism of the infusion flow control device and thecontainer.
 15. The system of claim 9 wherein the processor is configuredto sample the received signals in synchronization with movement of afluid control mechanism forming part of the infusion flow controldevice.
 16. The system of claim 9 wherein the processor is furtherconfigured to sample the pressure within the infusion line that connectsa primary and a secondary fluid container with the infusion flow controldevice.
 17. The system of claim 9 wherein the infusion flow controldevice comprises an infusion pump.